Line Substitution
ANGELES - APRIL 19: The Line Substitution Solution -- Pictured: Leonard Hofstadter (Johnny Galecki) and Howard Wolowitz (Simon Helberg). Sheldon hires Stuart to spend the day with Amy when he d rather

Johnny Galecki
only your brilliance, but your sense of humor will be sorely missed by all,” Johnny Galecki wrote in a tribute on Instagram — a sentiment echoed by cast mates Mayim Bialik

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